1. Field of the Invention
This invention relates to a lightning arrester for discharging electricity when an excessive voltage is imposed on an electrode in a container filled with insulation fluid.
2. Description of the Prior Art
"Gapless type" lightning arresters utilizing characteristic elements of zinc oxide are generally used for cubicle gas-insulated switching devices, as shown in Japanese Patent Publication (Kokoku) No. 58-11726 and Japanese Patent Disclosure (Kokai) No. 59-138089. An end of a series of characteristic elements is connected to an electrode in a gas filled cubicle or a container, and the other end is connected to ground voltage level. When the electrode voltage is lower than a threshold value, the electric resistance in the characteristic elements is infinity. If the electrode voltage rises higher than the threshold value due to lightning, the electric resistance decreases abruptly, and electricity discharges in the characteristic elements, protecting other devices connected to the electrode.
After on-site installation of a cubicle gasinsulated switching device has been completed, a withstand-voltage test is carried out in accordance with the technical standards for electrical installations. At this time, if the withstandvoltage is inadvertently applied to the arrester during the test, there is a possibility of the life of the characteristic elements being shortened or of insulation breakdown occurring. Therefore, the arrester should be isolated from the main circuit before the withstand-voltage test is carried out, and should be connected again after the test is completed.
The arresters disclosed in the above-mentioned references have the following problems. First, since the characteristic elements and an insulation tube containing the characteristic elements are all enclosed in the cubicle, the cubicle has to be large in height. Secondly, since there are sliding parts in the cubicle for connection and disconnection of the arrester to the main circuit, complicated structure is required for sealing the insulation gas.
Thirdly, it is difficult to check the performance of the arrester itself or to replace the arrester, because the insulation gas would leak out if the arrester is taken off the cubicle.
Japanese Patent Disclosure (Kokai) No. 59-40480 discloses an arrester with characteristic elements arranged and connected in a triangular position. The cubicle can be designed shorter using this arrester. However, the total volume of the arrester is the same. The construction is more complicated, and the above noted problems are still not solved.